The secretome of the environmental bacterium <i>Pseudomonas protegens</i> PBL3 has broad-spectrum antimicrobial activity against plant and human pathogenic bacteria

Antimicrobials are widely used to manage bacterial diseases in humans, pets, and livestock. Unfortunately, their extensive use has contributed to the emergence of antimicrobial resistance (AMR), a threat to global health. In contrast to the widespread antimicrobial use in medicine and veterinary, the use of antimicrobials to control bacterial diseases in plants is limited, posing a threat to global food security. These two threats highlight the urgent need to discover novel antimicrobial compounds with new modes of action. Previously, we demonstrated that the environmental bacterium <i>Pseudomonas protegens</i> PBL3 inhibits the growth of the plant pathogenic bacterium <i>Burkholderia glumae</i>, indicating that this strain produces and secretes potent antimicrobial compounds. In this study, we showed that the <i>P. protegens</i> PBL3 secretome also shows a broad spectrum of activity against plant pathogenic <i>Burkholderia</i> sp., as well as the human pathogens <i>Acinetobacter baumannii</i>, <i>Escherichia coli</i> O157:H7, <i>Listeria innocua</i>, <i>Enterococcus faecium,</i> and <i>Staphylococcus aureus,</i> with levels of growth inhibition ranging from 25% to 95% depending on the specific pathogen. These results highlight the <i>P. protegens</i> PBL3 secretome as a promising source of natural antimicrobial compounds with potential applications in both agriculture and clinical settings.IMPORTANCEThis work shows that the environmental bacterium called <i>Pseudomonas protegens</i> PBL3 produces and secretes molecules that have a broad spectrum of activity against pathogenic bacteria causing important diseases in plants and humans. The use of the collection of molecules that <i>P. protegens</i> PBL3 produces and secretes (secretome) instead of single molecules is likely to be more effective, as this collection of molecules is expected to be of diverse chemical structure and mode of action, which makes it less likely that pathogenic bacteria develop resistance to them. These findings highlight the potential of beneficial microbes as a sustainable source of broad and effective antimicrobials for both agriculture and medicine.